1. Field of the Invention
The field of the invention is that of digital radio.
To be more precise, the invention concerns a dual mode portable transceiver, i.e. a transceiver able to operate in either of two transmission systems, firstly a terrestrial radio network, for example a cellular network, and secondly a satellite radio network. One specific field of application of the invention is to GSM (Global System for Mobile communications) DCS 1800 terrestrial radio and Globalstar/Inmarsat satellite radio.
2. Description of the Prior Art
These two radio networks naturally have to use different frequency bands. The GSM DCS 1800 terrestrial system uses transmit frequencies in the 1 710 MHz to 1 785 MHz band and receive frequencies in the 1 805 MHz to 1 880 MHz band. The Globalstar satellite system uses the 1 610 MHz to 1 625.5 MHz transmit frequency band and the 2 483.5 MHz to 2 500 MHz band.
These different frequency bands require the presence, in a dual mode transceiver, of transmit and receive means specific to each mode of operation (terrestrial or satellite). This increases the cost, the overall size, the weight, and the power consumption of the receiver. These features are crucial to the design of a portable device, and a constant preoccupation is to reduce them.
If the frequency bands in question are close together, it may be possible to use the same transmit and/or receive means subject to some adaptation. This applies to the transmit frequency bands of the GSM and Globalstar systems, for example. On the other hand, if the frequency bands are relatively far apart (as is the case with the receive frequency bands of these systems), it is essential to use duplicate transmit and/or receive means, and in particular duplicate modulator and/or demodulator means. This leads to problems with weight, power consumption, etc.
One object of the present invention is to alleviate these drawbacks of the prior art.
To be more precise, it is an object of the invention to provide a dual mode portable digital signal transceiver for terrestrial and satellite radio, in which the increase in overall size, weight, and power consumption as compared with monomode (terrestrial or satellite) transceivers is small.
In particular, an object of the invention is to provide a transceiver of this kind which does not require duplication of all the receive and/or transmit subsystems, even when the relevant frequency bands are relatively far apart.